Gasification of solid carbonaceous materials



H. v. ATwELl. 3,009,795

GASIFICATION oF soun cARBoNAcEous MATERIALS Nov. 21, 1961 Filed Nov. l0, 1958 United States Patent O 3,609,795 GASIFICATIQN F SOLID CONACEOUS MATERIALS Harold V. Atwell, Wappingers Falls, NSY., assigner to Texaco Inc., a corporation of Delaware Filed Nov. l0, 1958, Ser. No. 772,38 2 Claims. (Cl. 418-206) This invention relates to gasification of solid carbonaceous materials. In one of its more specific aspects it relates to a process for the gasification of solid carbonaceous materials in finely divided form in a fluent solids system employing alternate partial combustion with air and gasification with steam in a series of zones.

In accordance with the invention a solid carbonaceous material, for example, coal, coke, or char, in fine particle form is heated to a high temperature by burning part of its carbon content with air, the hot solids after separation from the combustion products contacted with steam in a fluent system effecting reaction between hot carbon and steam to produce carbon monoxide and hydrogen, and the resulting partially gasified solids after sepwation of gas therefrom subjected to further combustion and steam gasification stages. The solid residue is finally 4burned with air in a zone of complete combustion and the combustion products are utilized to supply heat to the steam gasification zones.

The gasification of solid carbonaceous fuels by reaction with steam, lwith the heat of reaction supplied by burning a portion of the fuel with air, has long been known in the art of making water gas for use as fuel gas in cities and towns. in some water gas processes, a bed of incandescent coke is alternately blasted with air to supply heat and blown with steam to produce gas. Ordinarily these processes gasify coke in large fixed bed reactors. More recently solid carbonaceous fuels have been gasilied in large fluid bed reactors. ln fluid bed reaction systems, iiuidizing gas is passed upwardly through a bed of fuel in granular or fine particle form at a velocity sufficient to agitate the mass of particles without substantial entrainment in `the gas stream. In the usual operation, the mass of particles is maintained as a dense phase lluidized bed having a rather clearly defined upper level. The mass of particles in the lluidized bed resembles, in appearance, a boiling liquid. In such systems, one fluidized bed may oe used as the gasification zone wherein reaction between steam and hot carbon is carried out to produce carbon monoxide and hydrogen, while the other bed is used as the heating zone wherein part of the solid fuel is burned. Air is introduced into the burning zone to burn a portion of the carbon and heat the mass of carbonaceous solid particles to a temperature above the temperature necessary for the steamcarbon reaction, generally above -about 1400o F. Hot solid particles from the yburning zone are transferred to the gasification zone, where they supply heat for the gasification reaction of carbon with steam, while result ing cooled solid particles from the gasification zone are transferred to the burning zone for reheating. Such fluidized beds are characterized by a substantial amount of top-to-bottom mixing within the bed so that the composite in any section of the fluid bed is very similar to that in any other section. As a result, ash is not selectively concentrated in any part of the system, but dilutes the overall solid mixture so that large amounts of ash are in- 3,,795 Patented Nov.. 2l., 1961 ICC evitably transferred from one reactor to the other. In order to eliminate ash from the system, it is generally necessary to withdraw with the ash a considerable quantity of unreacted carbon.

It is one of the objects of this invention to provide a process for the gasification of coal in a fluent system which has a number of the advantages of the fluidized bed process described above and which eliminates some of the disadvantages of such processes. In the present process, the particles of solid carbonaceous material charged to the system are conveyed through alternate `combustion and gasification zones in series. The solid material progressively moves through the system until it is ultimately completely gasiiied.

The accompanying drawing is a flow diagram illustrating a preferred embodiment of the invention. Referring to the drawing, comminuted or particulate solid carbonaceous material is charged to a hopper 1li. This comminuted material preferably includes finely divided or powdered non-caking coal or char. The term charj as used herein refers to non-caking residual carbonaceous solid resulting from a partial oxidation or carbonization of a caking coal.

From the hopper lll, the fuel particles drop through conduit 11 into a heating zone 12 where it is mixed with and suspended in a stream of air introduced through line 13. The solid fuel particles suspended in air and the resulting gaseous combustion products flow through tubular heating zone 12. Heating zone 12 is preferably a horizontal tube capable of withstanding elevated temperatures in the range of 1300 to 2000 F. Alloy steel tubes, which may be provided with a refractory liner, may be used. The mixture of air and solid fuel particles is ignited within zone 12, either spontaneously or by means of a suitable igniter (not illustrated) and a portion of the fuel is burned, heating the solid fuel particles to a temperature above the temperature required for the steam-carbon reaction, i.e., above about 1300D F. Gaseous products of combustion together with the entrained heated solid particles are discharged from the heating zone 12 into separator 14. The gaseous combustion products are separated from the heated solid and discharged through line 16.

Heated particles of carbonaceous solid from separator 14 drop through line 17 into a tubular gasification zone 18 wherein they are contacted with steam introduced through line 19. The volume of steam is such that the particles are picked up and carried along through the gasification zone, which preferably is in the form of a horizontal, alloy steel tube. The steam reacts with a portion of the carbon in the hot carbonaceous solids during the passage through gasification zone 18, forming carbon monoxide and hydrogen. The resulting gaseous products `and residual, partially gasified carbonaceous solid particles are passed into separator 21 where gas is separated from the solid. The gas is discharged through line 22 as a product of the process.

Partially gasified particles from separator 21 drop through lines 23 and 23A into a second stage heating zone 24 into admixture with air entering through line 25. Sufiicient air is supplied to entrain the solid particles inair and resulting combustion products. The suspension of solid particles is heated in the second heating zone 25, preferably a horizontal, alloy steel tube witha refractory lining by burning an additional portion of the carbon from the solid particles. The proportions of air and solid fed to heating zone 24 are such that the solid particles are reheated to a temperature above the temperature required for the steam-'carbon reaction, i.e., above about 1300 F. The resulting heated solid particles suspended in gaseous combustion products are discharged into separator 26 wherein the heated solid particles are separated from the gases. The hot combustion products are discharged through line 27. Heated particles of solid carbonaceous material drop through line 28 into a second stage, tubular gasification zone into a stream of steam admitted through line 29. The volume of steam introduced through line 29 is sufiicient to entrain the solid particles and carry them along through gasification zone 31, preferably a horizontal, alloy steel tube. In the second stage gasification zone, an additional quantity of the carbon contained in the solid particles is reacted with steam to produce additional carbon monoxide and hydrogen. The product gases and residual solids from gasification zone 31 are discharged into separator 32 where product gas is separated from residual solid particles. Product gas is discharged through line 33; this gas may be combined with the gas from line 22.

Residual solid particles, now relatively low in carbon content and relatively high in ash, are drawn from separator 32 and fed through line 34 into combustion charnber 35 and subjected to complete combustion with air from line 36. Ash is discharged from combustion chamber 36 through line 38. Hot gaseous products of combustion passes through line 39 to furnace 41 surrounding the tubular reaction chamber 31. Combustion chamber 35 and furnace 41 may be contained within a unitary housing. The hot gaseous combustion products preferably tioW countercurrent to the direction of flow of reactants within the reaction zone. Part of the heat for the gasification reaction is supplied by indirect heat exchange between the hot combustion products and the reactants through the tube wall of gasification zone 31.

From heat exchanger 41, the hot gaseous combustion products iiow through line 42 to a jacket or furnace 43 surrounding tubular gasification zone 18. Preferably, the hot gaseous `combustion products pass countercurrent to the flow of reactants Within gasification zone 18. Combustion chamber 38, and furnaces `41 and 43 may be arranged within a unitary structure. The hot gaseous combustion products in furnace I43 supply a part of the heat required for gasification of carbon with steam in gasifer 18. Flue gases are discharged through pipe 44.

Gaseous combustion products from combustion chamber 36 are produced at a temperature well above the temperature existing in gasification zone 31. Gasifcation with steam is carried out at a temperature generally in the range of 1300 to 1800 P., suitably in the range of 1400 to 1600 F. Heat transferred through the Walls of tubular gasification zones 18 and 31 supplies part of the heat required for the endothermic reaction between steam and carbon in these zones. Flue gas from line 44 and gaseous combustion products discharged through lines 16 and 27 are at elevated temperatures, usually above about l400 F., and may be utilized in a suitable manner, for example, for the generation of steam, not illustrated in the drawing.

Residual solid carbonaceous material from gasification zone 18 may be recirculated to heating zone 12. As illustrated in the drawing, a portion of the residual solid from line 23 is drown through line 23B into a transfer line 46 where it is entrained in air introduced through line 47 and returned to gasification zone 12.

Air supplied to the heating zones may be preheated. Air preheat may effected, as illustrated in the drawing, by heat exchange with heating zones 12 and 24. A jacket 48 surrounding tube 12 serves this purpose. Air from line 49 is passed in countercuirent in direct heat exchange with the reactants within the heating zone 12, preheating the air and cooling the external surface of the tube wall of the heating zone. Similarly, jacket 52 surrounding the tubular wall of gasification zone 24 serves to preheat air from line 53 which may be supplied to second stage heating zone 24 through line S4.

The burning of carbonaceous fuel with air liberates heat at a very rapid rate; high velocities and air preheaters help prevent Alocalized overheating of the heating tubes. Steam may be added with the air to help control the temperature in the heating zone. The combustion products from the heating zones may have some fuel value, particularly where steam is added with the air, and may be used as low grade fuel for the generation of steam.

In carrying out this invention, as a specific example of a typical operation, non-caking coal or char having a particle size such that percent passes a 100 mesh screen and not over l5 percent is smaller than 200 mesh is subjected to gasification. The coal or char is partially burned with suicient air in the first heating zone at 20 p.s.i.g. to heat the gaseous and solid products to a temperature of about 1600 F. The heated solid particles at l600 F. are contacted with steam preheated to a temperature of l300 F. in a first gasification zone. The temperature at the Outlet of the first gasification zone is about 1250 F. Two thirds of the solids from the first gasification zone are recirculated to the first heating zone. The remaining solids from the first gasification zone are reheated in the second heating zone with air to about 1600 F. These reheated solids are passed to a second gasification zone into contact with 1300" F. steam. The hot particles of residue from the second gasification zone are completely burned with air in a combustion zone. Hot flue gases from the combustion zone at a temperature about 2000 F. supply heat to the second Agasification zone.

Generally, low superatmospheric pressures, e.g. 5 to p.s.i., are preferred, but higher pressures may be employed. Preferably the pressure Within the jackets surrounding the heating and gasification tubes is maintained near the pressure within the tubes, suitably diering therefrom only by the amount required to produce Ithe desired flow in the system. By equalizing or nearly equalizing the pressure inside and outside a tube or Vessel operating at high temperature and elevated pressure, the stresses on the tube walls can be greatly diminished. Air, steam, product gas, or inert `gas may be used for cooling the outside of the tube and equalizing pressure.

Steam for the gasification reaction is preferably preheated to at least 1000 F. and may be heated as high as 2000 F. Steam temperatures of 1200 to 1500 F. are preferred.

Obviously many modifications and variations of the invention as hereinbefore set for-th may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A process for gasification of ash-containing solid carbonaceous fuel in a plurality of substantially horizontal tubular heating and gasification zones which comprises suspending said solid fuel in finely divided particle form in a stream of oxidizing gas in a first heating zone effecting ignition and partial combustion of a portion of the oxidizable constituents therefrom and heating of said solid particles to a temperature above about 1200 F., separating gaseous combustion products from resulting heated particles of solid carbonaceous material, suspending heated solid particles from said heating zone in steam in -airst gasification zone effecting reaction between carbon and steam to produce carbon monoxide and hydrogen, separating gaseous products comprising carbon monoxide and hydrogen from partially gasified solid carbonaceous material, suspending partially gasified solid carbonaceous material from said rst gasification zone in a combustion supporting gas in a second heating zone effecting ignition and combustion of a portion of the residual carbon therefrom and reheating said solid particles, separating gaseous products of combustion from resulting canbonaceous residue, contacting said heated residue from said second heating zone with steam in a second gasification zone eiecting further reaction with carbon contained in said residue thereby producing additional carbon monoxide and hydrogen, separating gaseous products comprising carbon monoxide and hydrogen from resulting particles of carbonaceous residue containing said ash and residual carbon, subjecting sa-id residue from said second gasification zone yto substantially complete combustion, and passing resulting gaseous products of said cornplete combustion into indirect heat exchange with reactants undergoing gasification in said second gasication zone. l

2. A process according to claim 1 wherein said gaseous products of complete combustion are passed in heat eX- change with reactants undergoing gasification in -said rst and second gasification zones.

References Cited in the le of this patent UNITED STATES PATENTS 

1. A PROCESS FOR GASIFICATION OF ASH-CONTAINING SOLID CARBONACEOUS FUEL IN A PLURALITY OF SUBSTANTIALLY HORIZONTAL TUBULAR HEATING AND GASIFICATION ZONES WHICH COMPRISES SUSPENDING SAID SOLID FUEL IN FINELY DIVIDED PARTICLE FORM IN A STREAM OF OXIDIZING GAS IN A FIRST HEATING ZONE EFFECTING IGNITION AND PARTIAL COMBUSTION OF A PORTION OF THE OXIDIZABLE CONSTITUENTS THEREFROM AND HEATING OF SAID SOLID PARTICLES TO A TEMPERATURE ABOVE ABOUT 1200*F., SEPARATING GASEOUS COMBUSTION PRODUCTS FROM RESULTING HEATED PARTICLES OF SOLID CARBONACEOUS MATERIAL, SUSPENDING HEATED SOLID PARTICLES FROM SAID HEATING ZONE IN STEAM IN A FIRST GASIFICATION ZONE EFFECTING REACTION BETWEEN CARBON AND STEAM TO PRODUCE CARBON MONOXIDE AND HYDROGEN, SEPARATING GASEOUS PRODUCTS COMPRISING CARBON MONOXIDE AND HYDROGEN FROM PARTIALLY GASIFIED SOLID CARBONACEOUS MATERIAL, SUSPENDING PARTIALLY GASIFIED SOLID CARBONACEOUS MATERIAL FROM SAID FIRST GASIFICATION ZONE IN A COMBUSTION SUPPORTING GAS IN A SECOND HEATING ZONE EFFECTING IGNITION AND COMBUSTION OF A PORTION OF THE RESIDUAL CARBON THEREFROM AND REHEATING SAID SOLID PARTICLES, SEPARATING GASEOUS PRODUCTS OF COMBUSTION FROM RESULTING CARBONACEOUS RESIDUE, CONTACTING SAID HEATED RESIDUE FROM SAID SECOND HEATING ZONE WITH STEAM IN A SECOND GASIFICATION ZONE EFFECTING FURTHER REACTION WITH CARBON CONTAINED IN SAID RESIDUE THEREBY PRODUCING ADDITIONAL CARBON MONOXIDE AND HYDROGEN, SEPARATING GASEOUS PRODUCTS COMPRISING CARBON MONOXIDE AND HYDROGEN FROM RESULTING PARTICLES OF CARBONACEOUS RESIDUE CONTAINING SAID ASH AND RESIDUAL CARBON, SUBJECTING SAID RESIDUE FROM SAID SECOND GASIFICATION ZONE TO SUBSTANTIALLY COMPLETE COMBUSTION, AND PASSING RESULTING GASEOUS PRODUCTS OF SAID COMPLETE COMBUSTION INTO INDIRECT HEAT EXCHANGE WITH REACTANTS UNDERGOING GASIFICATION IN SAID SECOND GASIFICATION ZONE. 